This invention relates to a selector device for weft yarn presentation in shuttleless looms.
More specifically, the invention relates to a device for presenting the weft yarns to the grippers of shuttleless looms in which the various yarns carried into operation are presented within a narrow space interval to the gripper which inserts them into the shed.
To better illustrate the technical problem faced by this invention, together with the particular difficulties and requirements of shuttleless looms, reference is made hereinafter to the method of weft yarn presentation in such looms which is illustrated schematically in 1A,1B,2A and 2B.
FIG. 1A shows to the right the already produced fabric 1 and the shed open in the two planes 2 and 3 by the movement of the heddles, not shown in the figures for simplicity. Each time the shed opens, and with suitable synchronism, one or more weft yarns are inserted into it depending on the fabric pattern to be produced, this yarn or these yarns being delivered to a gripper 4 which is propelled and guided into the shed by a semirigid tape 5 which winds and unwinds with reciprocating rectilinear movement in the direction of the double arrow 6 by the effect of the reciprocating rotary movement, in the direction of the arrow 7, of lateral operating wheels 8 which are precision-controlled in terms of times, excursion and velocity. In the most widely used looms the weft yarn insertion gripper consists in reality of a pair of grippers which move starting from the two sides of the fabric, to meet in the middle where that gripper which has taken the yarn from the presentation device, and has completed its travel along one half of the width of the fabric, transfers it to the gripper on the other side, which turns back to complete its travel along the other half of the fabric width. The weft yarn inserted in this manner into the shed is incorporated into the fabric by the beating of the reeds, not shown in the figures for simplicity. During its reciprocating rectilinear movement the gripper 4 moves along the dashed-line horizontal trajectory 9.
The plurality of weft yarns which are to be inserted and woven with the warp yarns to form the fabric are contained on bobbins 10. FIG. 1A shows only four bobbins 19a, b, c, d for simplicity of drawing, however they are present in a greater number, generally eight but in certain cases more.
The weft yarn is presented to the gripper 4 by presentation rods 11a, b, c, d--again only four are shown for simplicity--which receive their weft yarn 12a, b, c, d from the respective bobbin 10a, b, c, d, after passage through the respective yarn feelers 13a, b, c, d. The presentation rods 11 are each provided with an end eyelet through which the respective weft yarn 12 passes. These rods can move between two positions, namely an upper rest position and a lower position in which they deliver the respective weft yarn to the gripper 4. In FIG. 1A the rods 11a, c, d are in their upper position and maintain the respective yarn out of range of the gripper, whereas the rod 11b is in its lower position in which it delivers the yarn 12b to the gripper 4 which is still retracted towards its propelling wheel 8 but is about to arrive at the position in which it grips the weft yarn.
The rods 11, for example the rod lib in FIG. 1B, move into their lowered delivery position to rest their yarn on a stop bar 14, so that the various weft yarns presented one by one to the gripper 4 lie in the generally horizontal plane defined by the upper edge of the bar 14 and the vertex 15 of the shed, in which region all the weft yarns of the fabric under production converge. By suitably adjusting the level of the bar 14, this plane can be made to contain the trajectory line 9 of the gripper 4, so that the gripper necessarily encounters the yarn presented to it at the appropriate time by one of the rods 11.
FIG. 1B schematically shows the situation after the yarn has been gripped by the gripper which has advanced along the line 9 towards the open shed. Downstream of the position in which the yarn is presented there is a cutting member 16, here indicated conventionally as scissors, which intercepts that portion of weft yarn lying between the moving gripper 4 and the vertex 15, to cut it with appropriate synchronism so that the weft yarn carried into the open shed is that which unwinds from its bobbin, and does not involve yarn on the same side as the already produced fabric. In FIG. 1A the scissors are shown open whereas in FIG. 1B they are shown closed with the yarn 12 cut. To better illustrate the requirements of gripper looms and the characteristics and advantages of this invention, reference will now be made to FIGS. 2A and 2B, which show respectively in transverse view and plan view the configuration shown in perspective view in FIGS. 1A and 1B, respectively.
FIG. 2A shows the rods 11a, c, d maintaining the respective weft yarns 12a, c, d raised, whereas the rod 11b is lowered with its yarn 12b resting on the bar 14. This yarn joins the edge of the bar 14 to the vertex 15. This configuration is shown in plan view in FIG. 2B, which shows the various lowered positions A, B, C, D in which the various rods 11 deliver their yarn to the gripper when they are lowered by the action of the presentation unit 17, consisting of a plurality of actuators 17a, b, c, d which lower and raise their rod 11a, b, c, d when it is the turn of their yarn, again considering that in effect the number of yarns, bobbins, yarn feelers and rods is greater, and normally eight or more.
As shown in FIGS. 1A, 1B, 2A and 2B, the rods 11 project with progressively increasing length and height from 11a to 11d, to maintain the various weft yarns at a greater distance apart when in their stand-by position. In this respect, each yarn to be presented must be lowered with reliability by operating its rod, without also presenting one of the yarns of the adjacent rods by the effect of the hairiness of or electrostatic charges on the yarns. As a result of this arrangement the points A, B, C, D representative of the plurality of weft yarn presentation members are shown as a segment inclined to the working line 9 of the gripper 4.
The delivery of the weft yarn is progressively more difficult from the first yarn 12a to the last yarn 12d, this number being shown for ease of drawing, however in fact they are of a greater number. As can be clearly seen from FIG. 2B, the yarn 12a is encountered by the gripper at the point A' and lies at a very acute angle to the trajectory 9, whereas the last yarn 12d is encountered by the gripper at the point D' and lies at a considerably less acute angle to the trajectory 9.
In this respect it must be noted that such a gripper 4 is currently constructed with the precise requirement of gripping only those yarns which it encounters at a narrow angle, whereas it does not grip any yarns which it encounters at a right angle or an angle which is not narrow. This requirement corresponds to the requirement that, should the shed not be perfectly open and any warp yarn is not completely raised or lowered, the gripper 4 must not grip it and pull it, but only shift it from its path, to raise it or lower it into the required position. Under such conditions those yarns more to the left in FIG. 2B have a greater probability of being gripped correctly, whereas the yarns more to the right have a greater uncertainty of correct outcome of the operation.
A further uncertainty in the proper gripping of those weft yarns more to the right on the drawing by the gripper is due to the fact that during gripping, the gripper is under considerable acceleration. It must be noted that in looms of the type under consideration, the frequency of the weaving cycle is currently of the order of 600-700 beats per minute and hence the gripper must travel from rest, arrive at the middle of the width of the fabric, halt with precision to deliver the yarn to the opposite gripper and then withdraw without yarn, all within a total time of less than one tenth of a second. Under such circumstances those yarns more to the right are intercepted by the gripper at a much higher speed than the yarns more to the left, they hence being more stressed and thus gripped with less precision.
The technical problem of improving the operation of presenting the weft yarn and the device which performs this weaving stage in gripper looms is hence essentially to shift the segment A'-D' towards the left and to shorten the length s. In FIG. 2B this represents that length of the gripper path along which the various weft yarns are presented. There is also the requirement to reduce as much as possible the width of the angle a which in FIG. 2B comprises the bunch of straight lines joining the point 15 to the points A-D, these representing the lowering of the weft yarn by the rods 11a-d for delivery, while however satisfying the requirement that when in the raised stand-by position the ends of the rods 11 must be properly separated so as not to also involve undesired adjacent yarns during lowering.